Sense amplifiers are necessary for circuits that require the discrimination of signals into signals of different states, i.e., a defined logical state "1" or a logical state "0." For example, these sense amplifiers are used in all integrated memory circuits for recognition of the digital state of a memory cell. Sense amplifiers can be used to determine the difference in the form of stored charges, cell currents or cell voltages.
In the article by Travis N. Blalock et al.: "A High-Speed Clamped Bit-Line Current-Mode Sense Amplifier," IEEE Journal of Solid State Circuits, Vol. 28, No. 4, April 1991, p. 42ff, a related sense amplifier is described for a CMOS memory cell.
A sense amplifier of this kind compares an input signal, for example, the discharge capacitance of a memory cell, to a reference signal. The reference signal, whose value is between the two logical values, can be supplied by a so-called dummy memory cell, for example. The sense amplifier compares the two signals to each other. The line with the greater signal is released and a power supply voltage is applied to the signal to be amplified. If a logical "1" is to be allocated to the amplified data signal, then a positive power supply voltage is applied to the corresponding output line by means of a semiconductor circuit, for example. Conversely, a negative power supply voltage or a reference ground voltage is connected to the output line when the amplified data signal is to be a logical "0."
Integrated semiconductor switches of this kind, which can be designed as MOSFETs for example, have a a typical threshold voltage of 0.7 V. Due to this threshold voltage, the particular power supply voltage will be applied to the data signal to be amplified with a time-delay. This so-called switching latency time corresponds to the time needed to drive the particular MOS semiconductor switch until it actually switches. Physically, the switching latency time represents the time needed for a MOSFET to form a channel. The switching latency time T.sub.D moves within a range of several ns to several .mu.s depending on the driving current of the gate electrode of the MOSFET.
The capability of today's semiconductor memories depends in particular on the speed that data can be read from or written into the memory. In particular, this performance of the memory is also determined by the capability of the corresponding sense amplifier.